RGBI files and infrared dust/scratch removal?

[sonora]

I'm starting to scan many color slides using a Plustek 8200 AI scanner. I want to scan in RGBI so that the infrared dust information is preserved (I channel).

Will Affinity Photo use the I channel info for dust removal? If so, how would I do this? I've searched and found nothing on point.

Mac Mini 2018 (Intel), 64GB, 2TB, RX 5700 XT GPU, Monterey 12.5.1, AP 1.10.5, Plustek 8200 AI, Vuescan 9.7.90, RGBI TIFF output files.

Thanks for any info you can supply.

[NotMyFault]

Hi and welcome to the forum.

Can you please upload an example file? If Affinity is able to read all channels of that TIFF, we can use the I channel as mask, e.g. for the Dust & Scratches filter.

I don't think the results will match the quality and comfort of specialised apps, but you will get more control.

[sonora]

Hi - I've attached an RGBI file, scanned at 3600dpi to reduce size. If AP can read the scanned infrared channel as an input for its dust & scratch filter, I'd like to compare that result with using AP's own filter.

Thanks very much.

scan0003.tif

[NotMyFault]

Thank you for this nice example file. Unfortunately it seems Affinity Photo ignores the extra IR channel.

Any chance you can export this channel from Vuescan separately, as grayscale layer? If yes, we could import it in Photo and use it as mask for the dust & scratches filter. Without such a mask, the filter does too much blurring for not affected areas.

Wikipedia articles explain a bit more about the technology. The methods used by Scanner apps do more tricks, as the IR channel and other RGB channels interact.

https://en.wikipedia.org/wiki/Digital_ICE

https://en.wikipedia.org/wiki/Infrared_cleaning

 

[Lisbon]

Is the infrared information supposed to be hidden?
I ask this because the image provided has only 3 channels.

[NotMyFault]

I expect the extra channels are marked as "ExtraSamples" of type 0 (unspecified) - or maybe as second page. The format might be vendor specific (beyond baseline tiff), and readers (apps) are advised to ignore those extra data (they have enough metadata to skip that).

 

from old tiff spec (search for TIFF6.PDF)

beware of extra components. Some TIFF files may have more components per pixel than you think. A Baseline TIFF reader must skip over them gracefully, using the values of the SamplesPerPixel and BitsPerSample fields. For example, it is possible that the data will have a PhotometricInterpretation of RGB but have 4 SamplesPerPixel. See ExtraSamples for further details.

 

 

ExtraSamples

Description of extra components. Tag = 338 (152.H)
Type = SHORT
N=m

Specifies that each pixel has m extra components whose interpretation is defined by one of the values listed below. When this field is used, the SamplesPerPixel field has a value greater than the PhotometricInterpretation field suggests.

For example, full-color RGB data normally has SamplesPerPixel=3. If SamplesPerPixel is greater than 3, then the ExtraSamples field describes the meaning of the extra samples. If SamplesPerPixel is, say, 5 then ExtraSamples will contain 2 values, one for each extra sample.

ExtraSamples is typically used to include non-color information, such as opacity, in an image. The possible values for each item in the field's value are:

0= Unspecified data
1= Associated alpha data (with pre-multiplied color)

2 =Unassociated alpha data

and:

https://www.hamrick.com/vuescan/html/vuesc24.htm

VueScan internally keeps all samples in 16-bit linear format, even when a scanner only supports 10-bit samples, but to minimize the disk usage, various TIFF file formats are supported:

1 bit B/W 1 bit per pixel 1 sample per pixel 1 bit per sample
8 bit Gray 1 byte per pixel 1 sample per pixel 8 bits per sample
16 bit Gray 2 bytes per pixel 1 sample per pixel 16 bits per sample
24 bit RGB 3 bytes per pixel 3 samples per pixel 8 bits per sample
48 bit RGB 6 bytes per pixel 3 samples per pixel 16 bits per sample
64 bit RGBI 8 bytes per pixel 4 samples per pixel 16 bits per sample
16 bit Infrared 2 bytes per pixel 1 sample per pixel 16 bits per sample

If you want to process the full bit depth of an image in Photoshop(TM), use the 48 bit RGB setting for the Crop TIFF file. Note that some other image editing tools cannot process 48 bit TIFF files; in this case use 24 bit which is more widely compatible.

 

 

So, no app beside VueScan may be able to correctly read these extra channels.

[NotMyFault]

If @sonora coul trick VueScan into saving in the last file format:

16 bit Infrared 2 bytes per pixel 1 sample per pixel 16 bits per sample

 

we may have a chance - unless it is saved again as "ExtraSamples"

 

PS: maybe this can help

https://www.pcreview.co.uk/threads/vuescan-does-saving-64-bit-rgbi-work-for-anyone.1937097/

Hello, Ed Hamrick
you wrote...

I just tried this in VueScan 7.6.80, and crop0001.tif was created
with all 4 channels (Red, Green, Blue, Infrared).

You might try deleting vuescan.ini and running VueScan again. Change
a minimal number of options when testing this, and then add in option
changes one at a time until the problem occurs. This will give you
the clue that's needed to diagnose the problem.

There are 4 channels saved, if Grain reduction and Infrared clean are
both set to None. If either one or both are set to Light, Medium or
Heavy output is limited to 3 channels.

[sonora]

Thanks, NMF & Lisbon. I appreciate your thoughts and resource pointers. I've only used Vuescan and Affinity Photo casually until now, and it's time to dig in. Since I'll be scanning (all too) many slides, I want to understand things thoroughly before I get rolling.